Signs That Indicate Planetary Gear System Replacement

The planetary gear system is an essential component of your final drive. It is a mechanical arrangement of several gears around a central axis.

The gears operate to provide sufficient torque to facilitate the smooth transportation of heavy loads. When it stops working, you can no more utilize it. This will lead to extended downtime and expensive repairs.

This article aims to facilitate you with essential information on failures of your final drive planetary gears. What causes them to fail? What measures can you exercise to avoid these failures? What are the key benefits of Planetary Gears? Sound Good? Read more to find out!


Planetary gear also refers to the epicyclic gear. The gear in this system is similar to that of planets around the sun. The gears replicate planets’ movement similar to that of the solar system. The main function of the planetary system is to reduce the rotation, which leads to higher torque in your final drive.

Several components or gears make up your planetary system. Some of the main components are as follows:

1.   Planet Gear Carrier

A planet gear carrier is the part of a planetary system that holds different gears with their centers of rotation. The design improves efficiency, reduces wear, and makes the machinery’s operation easier.

2.   Sun Gear

The inner shaft, which serves as the input shaft in the planetary system, serves the function of the sun gear.

The sun gear is a gear that employs mounting in the center of the planetary system. It transmits torque to the planetary gears placed in the surroundings.

3.   Dual Set of Three Planet Gears

These are two sets of three planetary gears that lie adjacent. They receive their rotational power mainly through the sun gear. The sun gear rotates clockwise while planetary gears rotate anticlockwise.

4.   Ring Gear

The ring gear also refers to the outer ring having a gear shape. The power from the sun gear reaches the ring gear through multiple planetary gears. When the process begins, the speed is higher at the sun gear while torque is less. On the other hand, the speed is low, and the torque is higher on the outer ring.

Apart from the components mentioned above, the other thing you need to consider is bearings. The time comes when they face wear and tear. If you cannot replace them in time, they will ruin your entire final drive system.

Visible Indications of Wear in Planetary Gears

The gears within the planetary system are responsible for force transmission as well as transmission of power and torque. These forces are high when teeth of gear mesh with each other. This is the point where you experience wear and tear.

The possible sign of wear and tear that you are going to see in your final drive are as follows:

1.   Worn-out Teeth’s

When the forces exceed their limit at the point where teeth mesh. Then the shape of the teeth begins distorting. A point comes where they change their shape from square to point. You can see the image for a better understanding.

2.   Bending in Gears Teeth

When a gear or gear train has incorrect gear tooth meshing, it will cause bending. It is also due to the high contact stress or the overheating of the material. The overheating results when frictional forces increase beyond the recommended limit.

3.   Cracking

Cracking in a gear’s teeth results from different stress states in the gear teeth. The primary causes are harsh conditions such as high speed, load carrying applications, and vibration. It mainly occurs at the base of the gear teeth.

4.   Surface Damage

Surface damage results when the teeth of gear get worn down by the elements over time. This includes elements such as dirt, sand, water, etc. The abrasive components or contaminated gear oil lead to pitting, scoring, scuffing, etc. They all lead to severe surface damage.

See the image as shown below. It represents what it looks like when your gear teeth are worn out. The following gear teeth face extreme wear and tear. Now it is not able to perform the meshing operation.

Also, please note if any abrasive or foreign particles exist in your planetary gear hub. It will lead to rapid wear and excess contamination.

The situation that the above image represents is horrifying. In this situation, no oil is within your planetary gear hub, representing an even worse scenario.

Additional Signs of Wear on Gear hub

It is unnecessary always to open your planetary hub to detect the issues. Sometimes you may detect malfunctioning without opening your gear hub. These signs or symptoms are as follows:

1.   Noise in Gear hub

Noise occurs in a gear hub when there is an excessive play between the teeth of gears. The noise produces when the gears start to rattle and even jump slightly as they slide against each other, creating friction.

When you hear new noises, it represents something messy with your final drive planetary gear hub.

2.   Vibrations in Gear hub

Vibration in planetary gear hub happens. This occurs when planetary gear’s speed and direction are not properly set to meet the application requirements. Material defects are present without countermeasures like lubrication, shimming, timing, and environmental factors.

How to Prevent Premature Failure?

You can practice several things to avoid wear and tear in your final drive gear hub. At least you can make it last longer with these preventive measures. Some of the most popular preventive measures are as follows:

1.   Timely Gear Oil Replacement

It is a very important and valid concern to consider when the gear oil in your gearbox starts to degrade. It is a cost-effective alternative to a reduction in overheating, friction, and low oil levels. Gear oil replacement also reduces contamination.

When you overcome these issues in your final drive-through gear oil replacement. This will result in longer life of your final drive.

2.   Avoid Leakage

Avoiding leakage is another preventive measure that will allow you to get rid of dirt, dust, debris, or foreign particles. This is mainly because of cracks within the components or damaged seals. They will let in these particles if not taken care of and cause abrasive wear and tear.

3.   Proper Alignment

When reinstalling the gear components in your final drive, align them properly. This will prevent you from premature failure of gears. Keep an eye on vibrations or sounds, do not ignore them. This is because they largely result from poor alignment.

Benefits of Planetary Gears

There are several benefits of a planetary gear system in your final drive. Some of the most common benefits are as follows:

1.   High Power to Weight Ratio

The higher power-to-weight ratio means the engine can apply more horsepower to a specific load. This can be beneficial in planetary gear systems.

As it allows for faster gear transmission and superior torque for longer periods. It increases the load carrying capacity of the unit.

2.   Compact Size

The compact size of the planetary gear system is beneficial in its ability to utilize less space and save time and money. Compact size improves the performance of the machine.

It helps to reduce fatigue and increase efficiency and productivity at lower costs. Compressed spacing between gears is more efficient than possible with conventional friction reduction mechanisms.

3.   Large Transmission

A large planetary gear system transmission transfers larger torque than its input torque. The larger the ratio, the better. This is because it reduces clutter from the overall interface.

This happens especially between an engine and transmission compared to a smaller transmission. It reduces the rate of speed of rotation. It also helps increase transmission efficiency by reducing inertia, mass, and friction.

4.   High Efficiency

The high efficiency of the planetary gear system is the ability to transfer energy. This happens from one section of a planetary gear assembly to another without losing its kinetic energy.

High efficiency can be beneficial. This is because it transfers more torque to rotating shafts that you can use to drive your machinery.

All of the benefits mentioned above determine its importance in your excavator. Therefore, you cannot ignore the importance of your excavator final drive planetary hub due to any means.


You better know all the indications that reflect your planetary gear system replacement. If you have any queries feel free to reach out.

Xugong has decades of experience designing and manufacturing planetary gear systems. So, you can trust that we’ll complete the job in the first go.

Whether you have broken gear, missed tooth, stripped shaft, or another common issue. You can trust us to repair your machine the right way.

We have the expertise and inventory to complete any job quickly and professionally. This guarantees 100% customer satisfaction.

Contact us now for more information about our services!


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